1. Field of the Invention
The present invention relates to a method and apparatus for detecting the amount of wire remaining in a wire bonder or a wire bonding machine.
2. Prior Art
As well known, in wire bonders, a bonding wire is kept wound around a wire spool. The wire is led out so as to pass through a clamper, etc. and then inserted into a capillary which is moved in a Z direction (vertically up and down) and also in X and Y directions (horizontally in any direction). The wire fed out of the wire spool is thus connected between first and second bonding points.
In conventional wire bonders, the remaining amount of wire on the wire spool is detected by several different methods. In one method, the initial length of the wire wound around the wire spool is stored in an arithmetic unit, which is a computer, etc., and the amount of wire remaining is detected by calculations performed by the arithmetic unit based upon the amount of wire consumed. In another method, a stretch of wire is detected so as to know the remaining amount of wire. More specifically, the wire in the area between the wire spool and clamper, etc. is stretched out straight when the wire wound around the wire spool runs out. Thus, by detecting the stretch of the wire of the last turn, it is able to know that all the wire has run out.
In the first method, however, consumption of the wire is not calculated unless the wire is used and actually connected between two bonding points. Accordingly, if a part of the wire is used for wire adjustment purpose (and not for actual connection or "wiring") which occurs when a wire spool is replaced with a new one, an accurate measurement of the remaining wire is not accomplished. In the second method, the stretching out of the last turn of wire is detected. However, use of the stretched wire during the "wiring" causes undesirable wire looping, and the products that use the undesirable wire looping are undoubtedly defective products.